The present invention relates to cyclically-operated hydraulic devices, and also to a method of operating such devices. The invention is particularly useful in liquid pulsators, such as now finding widespread use in water irrigation systems, and is therefore described below with respect to this application, but it will be appreciated that the invention could also be used in other cyclically-operated hydraulic device, such as externally-driven liquid pumps.
Pulsator devices, such as described in my Israel patents No. 74332, 88014 and 92886 (U.S. Pat. Nos. 4,781,217, 4,949,747 and 5,201,342, respectively) generally include an air-liquid chamber, an inlet having a flow-reducer for inletting the liquid into the chamber in a continuous manner at a low rate, and an outlet formed with a large orifice controlled by an outlet valve which opens at a relatively high pressure and closes at a relatively low pressure. Thus, the liquid may be continuously introduced into the air-liquid chamber at a low rate thereby increasing the pressure within the chamber, until the outlet valve opens, at which time the outlet valve discharges the liquid in the form of a pulse until the outlet valve recloses. Such pulsator devices are used in water irrigation systems to enable irrigation devices to be fed with water continuously at a relatively low rate but to discharge the water periodically in the form of pulses each pulse being at a relatively high rate.
During the operation of such pulsator devices, a small quantity of air from the air-liquid chamber is dissolved in the liquid pulse discharge from the chamber. As a result, after a relatively short period of continuous operation (e.g. about 12 hours), it is necessary to discontinue operating the pulsator device, permit it to drain, and then to be refilled with air, before resuming the continuous operation of the pulsator device.
The foregoing drawback is also present in other types of cyclically-operated hydraulic devices, such as externally-driven liquid pumps which include air-liquid chambers periodically discharging pulses of the liquid.